A conventional commercial aircraft generally includes a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes at least two aircraft engines, such as turbofan jet engines. Each turbofan jet engine is mounted to a respective one of the wings of the aircraft, such as in a suspended position beneath the wing, separated from the wing and the fuselage. Such a configuration allows for the turbofan jet engines to interact with separate, freestream airflows that are not impacted by the wings and/or fuselage. This configuration can reduce an amount of turbulence within the air entering an inlet of each respective turbofan jet engine, which has a positive effect on a net propulsive thrust of the aircraft.
However, a drag on the aircraft including the turbofan jet engines also has an effect on the net propulsive thrust of the aircraft. A total amount of drag on the aircraft, including skin friction, form, and induced drag, is generally proportional to a difference between a freestream velocity of air approaching the aircraft and an average velocity of a wake downstream from the aircraft that is produced due to the drag on the aircraft.
As such, systems have been proposed to counter the effects of drag and/or to improve an efficiency of the turbofan jet engines. For example, certain propulsion systems incorporate boundary layer ingestion systems to route a portion of relatively slow moving air forming a boundary layer across, e.g., the fuselage and/or the wings, into the turbofan jet engines upstream from a fan section of the turbofan jet engines. Although this configuration can improve propulsive efficiency by reenergizing the boundary layer airflow downstream from the aircraft, the relatively slow moving flow of air from the boundary layer entering the turbofan jet engine generally has a non-uniform or distorted velocity profile. As a result, such turbofan jet engines can experience an efficiency loss minimizing or negating any benefits of reduced drag on the aircraft.
In addition, some propulsion systems include an electrically-driven aft engine having an aft fan on the aircraft empennage to derive propulsive benefit by ingesting fuselage boundary layers. During operation, the inlet of the aft fan can see a strong swirl distortion due to upward flow from the bottom of the fuselage to the top. The swirl distortion can be detrimental to fan operability and can cause aeromechanical and/or operational issues.
Thus, an improved inlet assembly for an aft fan that addresses the aforementioned issue would be welcomed in the art. More particularly, an inlet assembly of the aft fan that reduces the swirl distortion would be especially beneficial.